Hydrophilic contact lenses can be formed from cross-linked polymers based on hydrophilic derivatives of acrylic or methacrylic acid, hydrophilic vinylic monomers such as vinylpyrrolidone, and the like. When hydrated, these hydrophilic cross-linked polymers can be referred to as hydrogels and include relatively large quantities of water without dissolving. Such polymers may include polymeric units derived from less hydrophilic, or even hydrophobic, monomers to confer mechanical strength and other useful properties.
End of the day discomfort is a condition reported by many hydrogel contact lens wearers. Discomfort associated with hydrogel contact lenses may be related to changes in water content or dehydration, changes in lubricity of a surface of the contact lens, or lens design, among other factors.